The invention relates to a method of controlling an automatic transmission with an electronic control system, and particularly of controlling hydromechanical transmissions and to a prognostic circuit for execution of this method.
All known control systems of this kind are operated in such manner that they determine the speed of the vehicle and the load on the vehicle, generally expressed as the output shaft RPM of the transmission. Then they determine the position of the throttle. If the prior given parameters are achieved, they give instructions to change-over the mechanical stages.
A drawback of this system is that if higher running resistances are encountered, a cyclic switching over of respective adjacent gear stages takes place. This is due to the fact that when running at a lower gear stage, the vehicle is accelerated up to a speed corresponding to the higher gear stage. The higher gear stage however provides for the vehicle a lower torque, which for certain running resistances can cause a deceleration of the vehicle and thus a repeated switching-over of gear stages until the running resistance decreases. These conditions generally prevail in the case of run-out, up grade running or in the case of a manual operation of the driver, i.e. up to a forced switching to a lower gear stage. The cyclic frequency is higher with lower hysteresis between the requirement for switching to a higher or lower gear stage. An increase of this hysteresis, however, makes the optimum selection of the moment of switching difficult.